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cheddarhead 02-08-2007 11:23 AM

Carrier Furnace - out cold :)
I have a model 398AAW Plus 90 Carrier furnace. It quit working yesterday - nice and cold day to go out. Well, I thought it might be a transformer problem, so I replaced the 24volt/40watt transformer in the control box. Same problem. The inducer motor spins freely when nudged with a small screw driver. Today I replaced the control board with a new one. Went from a version 015 to a 021 board. Now the furnace will start up, run for a couple seconds then shut off.

What do I do next?

#CARRIERMAN 02-08-2007 11:29 AM

Hi cheddarhead

Locate the flame sensor, shut the power off to the furnace. The flame sensor will have a single 1/4" screw in it. Remove the screw use a piece of steel wool, scotch brite pad or a wire brush and clean. Reinstall the flame sensor and see if this fixes your problem.

Good luck

cheddarhead 02-08-2007 12:02 PM

Did not see it
I looked for a single screw device - did not see any... Any tips?
I found a device connected to a circuit board behind the gas valve. Two leads going to that. Removed it and gently brushed it off. No change.:(

#CARRIERMAN 02-08-2007 12:36 PM

Hi cheddarhead

I am sorry, the piece you need to pull out will be a stainless steel rod inside the burner compartment. I should have clarified myself a little better.

Good luck

cheddarhead 02-08-2007 04:03 PM

No biggee
Thanks for the replies... By all means feel free to clarify all you want... I am a bit of a newby to all this...

Is this piece under the spark ignitor access? (see, I am a newby)

#CARRIERMAN 02-09-2007 08:55 AM

Hi cheddarhead

Locate the burner box. This is the area with one or two little plastic windows in it, you will normally see flames while the furnace is running in these windows. If you look around the outside of the burner box you will see a piece of procelin with two white wires coming out of it, this is the ignitor. Just opposite of the ignitor will be a porcelin piece with a single white or yellow wire coming off of it, this will be the flame sensor. Please be sure to shut power off to furnace before attempting any kind of a repair.

Good luck

cheddarhead 02-09-2007 01:14 PM

This does not look like that
Hi Rusty!

Well, I took a look for the flame sensor. What you describe is not immediately visible. There is a gas jet for the ignitor, I assume. On that device is a porcelin device like you mention. There is a single RED (big fat red) wire going to it. That wire goes back out to the spark ignitor a bit lower inside. There is another connector there, with three wires. A white, a green, and a yellow. Those wires go back out to the gas valve. There is a component in-line - a diode? a fuse? Could that be an issue?


Brik 02-09-2007 03:46 PM

Time to call the repair man if you are getting cold. :)

cheddarhead 02-12-2007 11:47 AM

Someone suggested replacing the entire gas ignitor / flame sensor assembly. Does thismake sense to you?

BTW - I have secondary heat.. In case Brik wanted to know...

jbac 02-13-2007 05:39 PM

yes sir indeed

cheddarhead 02-13-2007 06:57 PM

How to test ignitor...
Do you know if there is a way to test the ignitor itself? With a multimeter, or voltmeter?

#CARRIERMAN 02-19-2007 03:00 PM

Hi cheddarhead

Sorry I haven't been back to help, I am in the middle of becoming a railroad conductor. Man is this schooling tough. The problem with your furnace is the pilot burner assy. You will need to replace the pilot burner assy if it cannot be cleaned. I would suggest pulling it and cleaning it out. If you have to replace it they are pretty pricy. The part number for your pilot assy. is a LH680005. Sorry it took so long to respond, if you have figured it out already just disreguard this post.

Good luck

cheddarhead 02-19-2007 03:32 PM

Is there any reason to suspect the ignitor is bad? Is there a way to test that as well? with a multimeter/volt meter?

harleyrider 02-20-2007 07:36 AM

Watch the unit as you have someone turn the termostat up, there should be a breif period were you hear the spark box sending a spark to the pilot (TIC TIC TIC TIC ) then the pilot should light. As the pilot burns it heats up a bi-metal strip, the pilot flame itself should be blue and strong. After a period of time the main gas valve should open and all the burners should lite.

Is any of what I decribed in detail to you taking place?

cheddarhead 02-20-2007 05:33 PM

Hey, thanks for the reply. No, there is no snapping sound at all. That is why I asked about the ignitor. The previous post seems to indicate the pilot assembly, but I want a means to verify the ignitor so I do not chase one problem, only to find it is another instead...

The furnace fan turns on, runs for 2 - 3 seconds, then shuts off. I never see a flame of any kind or hear any snapping sound from the ignitor...

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